First Presbyterian Church

Landmark Building Rehabilitation

First Presbyterian Church, popularly termed the “fish church” for its distinctive shape, was designated a National Historic Landmark in 2021. Designed by legendary Modernist architect Wallace K. Harrison, the iconic 1958 building was suffering from persistent water infiltration that had defied a number of repair efforts. Hoffmann Architects + Engineers was retained to diagnose and correct the leaks, as well as restore damage to structural and finish elements caused by the constant presence of moisture.

The project team confirmed that alkali-silica reaction (ASR) was one cause of the substantial concrete cracking. ASR occurs when high-silica aggregates in the concrete mix react with water to form a gel, which expands. The outward pressure leads to cracks, eventually destabilizing the concrete. To protect against further degradation, Hoffmann’s design professionals specified an elastomeric coating to keep the concrete dry, following repair of cracks and spalls.

At intersections between concrete and dissimilar materials, such as slate or metal flashings, sealant deterioration was admitting water into the structure. Broken slates, flashings worn by acid rain, and damaged glass acted as further points of water entry.

Successful rehabilitation demanded experience in materials ranging from historic to technologically sophisticated, all used in unconventional ways. Hoffmann designed and oversaw a series of repairs that eliminated sites of moisture intrusion to protect against future degradation.